State and local officials are taking strong steps in response to the largest U.S. measles outbreak since 2000. In California, staff and students at UCLA and California State-Los Angeles were required to stay home after an outbreak there. Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, joins Judy Woodruff to discuss how to achieve measles immunity.

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Judy Woodruff:

This is precisely what public health officials were trying to avoid. The U.S. is now dealing with the worst outbreak of measles since 2000. There have been nearly 700 cases confirmed in 22 states this year, mostly concentrated in a handful of places, New York, California, Washington state, Michigan and New Jersey.

In California, one of the most sweeping efforts yet to deal with this, Los Angeles officials this week quarantined more than 900 students and faculty at two universities. Students and staff from UCLA and from California State University are required to remain at home or in their rooms.

And, today, President Trump called for unvaccinated children to get immunized.

Dr. Anthony Fauci is the director of the National Institute of Allergy and Infectious Disease.

Dr. Fauci, welcome back to the "NewsHour."

So, the first question is, what is the source of this outbreak of measles? What's going on?

Dr. Anthony Fauci:

Well, it's almost always someone coming in from out of the country or someone visiting a country in which they have measles that's pretty much prevalent.

And they bring it back into a community in which there's a low level of vaccine protection. That's exactly what we saw in the major outbreak that's going on right now in the Williamsburg section of Brooklyn in New York City, in that you had a community that was very low in the degree of protection.

You need about 93 to 95 percent of the community to be vaccinated in order to get that blanket of protection.

Judy Woodruff:

And with regard to these colleges in California, why was the quarantine necessary? Couldn't they just assume that most everybody has been vaccinated?

Dr. Anthony Fauci:

I think they will make that assumption. That's a reasonable assumption. What happened was that the student who went to the different classes and exposed individuals, the reason they do that right away, Judy, is that measles is clearly one of the most contagious viruses known to man.

And the very fact that one is in a room with someone even for a relatively short period of time puts them at high risk. So what the officials at the college wanted to make sure that, first of all, to go through the students, screen them and find out if there was documentation that they were vaccinated. Then they would be fine.

If it was unclear whether they would be vaccinated or not, then you might have to keep them a bit longer through that incubation period. So I think they did the right thing.

Judy Woodruff:

Well, something that caught my eye, and that is that more than three-quarters of measles patients in California had either not been vaccinated at all or had gotten only one of the two doses recommended, but that means that another quarter of these measles patients had been vaccinated. But they still got measles.

Dr. Anthony Fauci:

Yes, what happened is there are situations where a person may have gotten vaccinated, but the real, true protection that you get that's 97 percent is, you get two doses, one at 12 to 15 months, one at four to six years.

So there may be people there who either got a single dose and are not fully protected, or the vaccine didn't protect them.

Judy Woodruff:

As we reported, the United States now has the highest number of measles cases since the disease was supposedly eliminated in 2000.

What does that mean for the people who live in one of these 22 states or anywhere, for that matter? What should they do to protect themselves?

Dr. Anthony Fauci:

Well, there are two things.

One, when you get cases, they need to be isolated and keep people segregated away from the people who clearly have measles.

But getting back to the first order of business is to make sure you're up to date on your vaccinations. And that's the message we really want to get out to people. If you have good documentation of your vaccination, you're fine. If you have been born before 1957 or an older individual, it is likely that you were infected with measles. You're OK.

If you're not sure of what your vaccination status is, then what you need to do is a couple of things. If you're an adult, get vaccinated with the measles, a single shot, because there is really no harm in doing that, or you can go to a physician and find out if you're immune.

But the bottom line of all of this, Judy, is to just make sure we vaccinate our children and, if you're an adult, to check and see if you have had the full component of the vaccinations.

Judy Woodruff:

And I was reading today that, for some people over the age of 30, it may be necessary to get another measles vaccine.

Dr. Anthony Fauci:

Well, it depends on who you are. If you have had a single shot and you're not living in an area where there's a clear outbreak, you're OK.

But if you're in an area where you're at risk, even if you have had one shot, it's recommended that you get a booster shot.

Judy Woodruff:

And, finally, how do you view the fact that many people are still protesting against having measles vaccinations? They have thousands of people protesting in California this week.

Dr. Anthony Fauci:

It's really — it's unfortunate, Judy, that we have that mind-set that, even now, with the demonstration that this is a very contagious disease, the misinformation that this is a vaccine that causes serious adverse events like autism, which it definitely doesn't, and the manifestation that right now in real time we're seeing outbreaks, to still protest about getting vaccinated is something that's just beyond explanation, I believe.